Variable current thermal responsive device



July 12, 1949. R. M. BENNETT 2,476,022

l VARIABLE, CURRENT THERMAL RESPONSIVE DEVICE Filed June 21, 1945- Inventor: Robert M. B ehn ett,

by H i5 Attorney.

malas my Iz, 1949' VARIABLE cUaaEN'r THERMAL RESPONSIVE oEvrcE Robert M. Bennett, Birmingham Township, chester County, Pa., assigner to General Electric Company, New York, N. Y.

Application June 21, 19475, Serial No. 600,669

14 Clliml.

My invention relates to variable current thermal responsive devices. more particularly to current responsive trip means for circuit breakers and has for its object a simple, reliable and shockproof relatively high and low current responsive trip mechanism.

To carry out my invention in one form I provide a. thermal responsive element in lthe form oi' a tension rod having a high temperature cueillcient of expansion, and heat the rod by means of two bare tubes made of electric resistance material which surround the rod in concentric nested relation with each other and -with the rod, the tubes being radially spaced in electrically insulating relation with each other except at one end. The two tubes are secured electrically and mechanically together at adjacent ends while the opposite ends of the tubes are provided with electric connection means whereby the tubes can be connected in series with each other in circuit with the circuit breaker.

'Ihis heating resistor in the form of the two series connected tubes provides for the eiiicient transfer of heat to the rod and also provides -for the independent adjustment of the heating effect thereof under both low overload current and high overload current conditions. Preferably I arrange the inner resistor tube to generate sufiicient heat in response to a high current so las to heat the rod in a relatively short time for quick opening of the circuit breaker. Under high current tripping conditions the heat generated in the outer tube does not have time to be transferred appreciably to the inner tube and thence to the rod. For long time, low current tripping the total heat generated by the two heaters is utilized and the cross section and resistivity of the outer tube can be adjusted to give the desired total heat under low current conditions without substantially affecting the short time high current operation.

One end of the thermally expansive rod is fixed while the other end is connected to a trip member which is biased by a spring to a circuit breaker tripping position but normally held by the rod under tension in a circuit breaker closed position. With this arrangement all clearances or lost motion in a tripping direction are taken up by the spring so that a shock can take up lost motion only in the opposite or non-tripping direction.

For a more complete understanding of my invention reference should be had to the accompanying drawing wherein Fig. l is a side elevation view with the cover broken away ot -a thermal tripping mechanism for a three pole circuit breaker viewed from the circuit breaker side, Fig. 2 is a sectional view of Fig. l taken along the line 2--2 of Fig. 1 looking in the direction of the arrows and showing a. typical circuit breaker associated therewith by dash lines, Fig. 3 is a fragmentary view in perspective showing features of construction, and Figs. 4 and 5 are fragmentary views in section showing modified forms of my invention.

Referring to the drawing I have shown my invention in one form as applied to a three pole or three circuit circuit breaker l of the manually operated type such as described and claimed in application, Serial No. 555,630, filed on September 25, 1944 by John A. Favre and assigned to the same assignee as this invention. The circuit breaker I is indicated by dash lines in Fig. 2. The thermal trip mechanism is the same in each of the three circuits and, in view of the fact that the middle thermal trip mechanism 2 is mounted adjacent the latch means securing the circuit breaker normally in its closed position, only this middle mechanism 2 will be described in detail.

Referring to Fig. 2, the middle thermal mechanism 2 comprises a U-shaped supporting member 3 made of a non-magnetic metal, such as brass, which has its base 4 secured in an upright position to an upright supporting wall or base 5 made of a suitable electrically insulating material, such as molded phenolic condensation produ ct. Mounted on the U-shaped member 3 are two concentrically arranged bare tubular heating resistors 6 and l and a thermally expansible rod or wire 8 which extends through the inner and smaller heating tube 1. The tubular heaters e and l, made of a suitable resistance heating material, are mounted in a suitable radially spaced relation with each other, the spacing, of course, being determined by the relative diameter of the tubes, and the rod 8 while closely tting in the bore of the inner tube l is in substantial spaced electrically insulating relation with the inner tube. Preferably the rod 8 is made of a high resistivity material as compared with the tube l so that direct contact between them does not divert any substantial amount of current through the rod from the tube.

At their upper ends the tubular heaters `6 and 1 are electrically and mechanically secured together, as shown by spinning the upper end of the larger tube -6 onto the upper end of the inner tube and brazing the two ends together. The two tubular heaters can be connected in circuit with the circuit breaker by means of a terminal connector I brazed to the lower end of the outer tube and a terminal connector II brazed to the lower end of the inner tube. As shown, the inner tube extends downward below the lower end of the outer tube for connection with connector Il and also a sufficient distance to provide for a U- shaped magnet core I2, shown as laminated. which rests at its opposite sides on inwardly turned projections I3 and I4 on the lower ends ofthe sides of the support 3. Also the projections |3 and I4 form the supports for a U-shaped cross member I5, made of non-magnetic material such as brass, having its ends secured to the projections, as by riveting. In the center of this member l5 is secured a stationary nut I5 for receiving the lower threaded end of the rod 8 whereby the lower end of the rod is secured in a fixed position relative to the other movable parts. As shown in Fig. 2, the nut I5 extends through an aperture in the member I5 in spaced relation with the walls of the aperture. It is provided with an upper flange while its lower end is peened over on a washer I1, washers I8 of electrically insulating material being provided between the top flange and the member I5 and between the washer I1 and the member I5 -whereby the nut I6 and the rod 8 are electrically insulated from the member I5.

As shown, the connector I0 forms a flange on the lower end of the tubular heater 6. This ange rests on electrically insulating washers I9 seated on the magnet core I2. Upward movement of the tubular heaters is prevented by the engagement of the connector I0 with the upper wall of the notch in the support 5 through which the connector I0 extends.

The thermal trip mechanism 2 cooperates with a metal trip shaft 2| which extends across the other two mechanisms 22 and 23, the shaft being supported by a bearing 24 formed in a bracket secured to the lefthand side of the support 3, as viewed in Fig. 1, and in a second bearing, not shown, in a second bracket 25 secured to the righthand side of the support 3. At its center the shaft is cut away somewhat more than half way through its diameter to form two flat surfaces 26 and 21 parallel with the axis of the shaft and at a small angle with each other. An arm 28 has its end just above the righthand side of the surface 21, as seen in Fig. 3, so that when the end of the arm is moved downward upon thermal expansion of the rod 8 the shaft 2| is turned in a clockwise direction, as seen in Fig. 2, against the force of a counterclockwise biasing spring 28' sufficiently to disengage the righthand latching edge ofthe surface 26 from the latch member 29 whereupon the circuit breaker I opens in accordance with its bias.

As shown in Fig. 3, the left hand end of the arm 28 is bent around to provide a parallel arm 29 thus forming a U-shaped portion, each side of which is provided with an aperture through which extends a pivot pin 30 having its ends secured in the sides of the support 3. By means of a spring 3| the arm 28 ls biased in a clockwise direction about the pin 30 with its U-shaped lefthand end bearing against the projections or pins 32 and 33 extending from opposite sides of a member 34 having an aperture through which the rod 8 extends. Thus the member 34 is forced upward by the spring 3| against a pair of adjustment nuts 35 on the upper end of the rod 8. By adjustment of the position of the nuts 35 the position of the righthand end of the arm 28 with respect to the surface 21 can be adjusted thereby to adjust the current value at which the shaft 2| is turned. As shown in Fig. 2 the pivot pin 30 has a portion cut away at a point adjacent the member 34 thereby to provide increased clearance.

The spring 3| provides the operating force to turn the shaft 2| upon thermal expansion of the rod 8, this spring 3| being much stronger than the biasing spring 28 for the shaft 2|. This construction is of importance in making the trip mechanism free from the effects of high impact shocks and from vibration for the reason that the spring 3| in applying a force to the arm 28 in a clockwise tripping direction thereby takes up all lost motion between the parts in a tripping direction, particularly the clearances with respect to the pins 30, 32, and 33, the rod 8 acting to restrain the arm 28 against movement by the spring 3| under normal current conditions. Therefore, any movement of the arm 28 resulting from the effects of shock or vibration must be in a non-tripping direction, and false tripping in response to a shock or vibration is prevented.

By means of the magnet core I2 a quick release action before the rod 8 is heated sufficiently is obtained in response to very high currents, the magnet then being energized sufficiently to attract the lower end of an armature 36 which is pivoted on a stationary rod 31 having its ends secured to the sides of the U-shaped support 3. The armature is constructed with its weight substantially balanced about the pivot 31. It is biased counterclockwise, as seen in Fig. 2, by means of a helical spring 38 having one end secured to a suitable stop (not sho-wn) on the support 3. When the current in the inner tubular heater 1 reaches a predetermined high value which preferably is of short circuit magnitude, or at least higher than overload currents or the normal circuit transient currents such as those caused by motor starting, the lower erossportion 39 of the armature is attracted by the magnet core and pulled into engagement with the two magnet pole faces 40 and 4I, indicated by the dotted lines in Fig. 1. During this movement of the armature, a pin 42 (Fig. l) carried on the upper end of the armature moves into engagement with a projection or arm 43 made of electrically insulating material secured to the rod 2| whereby the rod is turned clockwise as viewed in Fig. 2 to trip the circuit breaker. Adjacent the projection 43 is a second projection 44 made of electrically insulating material secured to the rod and attached to this projection is the helical spring 28 which biases the shaft 2| counterclockwise against a suitable stop, as shown with the left hand end of the surface 21 resting against the end of the arm 28.

The two projections 43 and 44 are integral with a member 46 made of a molded electrically insulating material surrounding the shaft 2| and secured rigidly to the shaft. This member 46 and the projections are preferably molded directly on the shaft.

On the left hand end, as seen in Fig. 1, of the shaft 2| is secured a second member 41 made of molded electrically insulating material and provided with a projection 48 arranged to be engaged by pin 49 on the armature 50 of this left hand. trip device and with a trip projection 5| bearing against the trip arm 52 corresponding with the arm 28 of the middle trip device. A member, not shown, similar to member 41 acuosa with similar projections is provided on the opposite right hand end of the shaft 2| for the right hand trip device. These right hand details are not shown because they are concealed by a portion of the cover 53.

For the purpose of preventing manually the rotation of the shaft 2| so that the circuit breaker will remain closed regardless of the value of the current in it, an arm 54 is provided which may be depressed by a button 55 to bring its end 56 into engagement with the flat surface 26 which acts as a stop. In moving to this position, the curved end portion 56' of the member engages the curved upper end of the latch member 29 and thus acts as a stop to prevent movement of the latch member 29 in a counter-clockwise direction, thereby manually preventing opening of the circuit breaker..

Preferably, the curved surface 56' engages the upper curved end of the latch member 29 somewhat before the arm 5t reaches its lowermost position so that the latch arm 29 is turned slightly in a clockwise direction out of engagement with the shaft 2 I. This assures the locking of the latch arm 29.against counterclockwise opening movement. Therefore, by holding the button 55 depressed, the circuit breaker can be maintained closed regardless of the value of the current through it.

The arm 54 is pivoted at its iefthand end as seen in Figs. 2 and 3 on the pivot pin 30. It is held in its raised position, as shown in the drawing, by means of two leaf springs 51. The righthand ends of the leaf springs are provided with an elongated aperture through which extends a projection 58 on the arm 54, the springs being secured on the projection 58 by the lower ends 59 of the button which embrace the projection 58 and are pivotally secured to the projection. The outer or righthand ends of the springs rest on the end of the arm 54 while the lefthand end of the springs rests on the cross portion 6|] of the spring 3|. It will be observed that the spring 3| has two end helical portions encircling the pivot pin 3D while the ends of the spring rest on stop pins 6I and 62 secured to the support 3.

For the purpose of securing the insulating base 5 on the circuit breaker base, not shown, projections 63 and 64 are provided on the base 5. These projections extend forward, as seen in Fig. l, between the trip devices.

Referring to Fig. 2, when the shaft 2| is turned clockwise to release the pivoted latch member 29 mounted on a pivot 65, the latch member 29 is turned against the bias of spring 1| through a, limited angle in a counterclockwise direction due to the preponderant force exerted on a suitable second pivoted latching member 66 by the strong opening bias of member 68 of the circuit breaker I that forces member 66 to turn counterclockwise about a pivot 61 with the upper end of member '66 moving underneath the latch member 29. This frees the circuit breaker member 68 which engages and is normally held by the latch member 66 whereby the member 68 moves upward in accordance with its predominately strong opening bias and permits the circuit breaker I to open. When the circuit breaker is again reclosed the member 68 is moved downward and engages a projection 69 on the latch member 6B thereby turning the member 66 back to the position shown in Fig. 2 with a roller 10 carried by the latch member 66 engaging an upwardly extending projection on the end of the member 68 whereupon the spring 1| turns the latch 29 clockwise back to 6 its latching position in engagement with the latch 66. The shaft 2| is then rotated counterclockwise by the spring 28' to bring the righthand edge of the face 26 into latching engagement with the latch member 29, as seen in Fig. 2.

An advantage of this trip mechanism, especially of the heating means-for the expansible rod 8, is that the tubular heaters can be constructed substantially independently of each other to adjust as desired the high current tripping value and the long time low current tripping value. The high current short time tripping ls produced almost entirely by the inner heater 1 because heat from the outer heater 6 does not have time to be transferred to the rod 8. Therefore, the high current short time tripping depends upon the cross section and resistivity of the inner heater 1, the crosssection of the rod 6 and the distance or spacing between the heater 1 and the rod 8.

The long time low current tripping current depends upon the total heat generated by the two heaters because in this case the time is great enough for heat to be transferred from the outer heater 6 to the rod 8 as well as heat from the inner heater 1. Consequently, the cross section and resistivity of the outer heater can be adjusted to give the desired total heat for tripping at the desired current without substantial effect on the high current short time tripping.

Another advantage of the concentric tubular heaters is the prevention of distortion of the heaters by the magnetic forces set up by extremely high currents or short circuit currents. This is because of their tubular shape whereby the stresses applied to the heaters by the magnetic forces are in radial directions and tend to balance each other.

Moreover, the tubular construction of the heaters supplies a minimum outside area, i. e. the outside area of the outer tubular heater 6, for the dissipation of heat to the surrounding and adjacent parts. Therefore, the thermal element can operate at a very high temperature without objectionably increasing its ambient temperature or the temperature of adjacent parts of the device.

The arrangement of the expansible rod 8 and the metal support 3 provides for compensation for ambient temperature changes to a great extent depending upon the relative temperature coeilcients of expansion of the metals of the support 3 and the rod 8. If these coeicients are the same for the metals of the support and the rod, then the device is completely compensated for changes in ambient temperature, since a change in the length `of one would be offset by the same change in the length of the other, both being subjected to the same change in ambient temperature. The arm 28 would then be responsive to the elongation of the rod 8 caused by a temperature higher than the temperature of the support 3. In a typical device, however, the rod 8 has a higher temperature coefficient of expansion than the metal of the support 3, and, consequently, the trip mechanism is not completely compensated for ambient temperature changes, although substantially so.

In Fig. 4 I have showna modified form of my invention in which a single tubular heater 12 is provided having one end electrically and mechanically connected to one end of the thermal expansible rod 13 which is tubular, as by a welded or brazed joint 14. The rod 13 corresponds to the rod 8 of Figs. 1 to 3, inclusive, and is connected to trip mechanism in the same manner as 15 rod 3. A terminal connector 15 is provided for the opposite stationary end of the rod 13 and a connector 18 is provided for the opposite end of the heater tube 12. Therefore. with this arrangement current passes through the rod 13 itself whereby the rod is heated by heat generated in it, and through the heater tube 12 in series with the rod.

Preferably, the rod 13. and also the rod 8 oi' Figs. 1 to 3 inclusive, is made from a material having a high coefficient of expansion, such as an alloy consisting oi 72 percent manganese. 18 percent copper, and 10 percent nickel. This material also has a high electrical resistivity for the generation of heat when current is passed through it. The high resistivity characteristic is of advantage in the construction of Figs. 1 to 3 inclusive, in which direct contact between the rod 8 and the heater tube 1 in a typical device did not divert any substantial amount of current from the heater tube 1 which was made of a lower resistivity material.

In the modified form of my invention shown in Fig. the two concentric spaced tubular heaters 11 and 18 are heated inductively by a coll 19 connected in circuit with the contacts of the circuit breaker. As shown, the two tubes 11 and 18 are joined together at their upper ends to provide a support for the outer tube, while the inner tube encircles one leg of the U-shaped magnet core 80. The expansion and contraction of the inner tube 18 is utilized, the lower end of the tube being stationary and its upper end having an extension 8l arranged to engage and operate suitable tripping mechanism for the circuit breakers, such as that shown in Figs. 1 to 3 inclusive. Also, the tripping mechanism is operated in response to short circuit currents by a pivoted armature 82 for the magnet core.

While I have shown several embodiments of my invention, it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made and I therefore contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1.. A relatively high and low current responsive device comprising an elongated current conducting heater member, a tubular current conducting and in a longer time interval to the joint heating effects of both heaters when the current is relatively low.

2. A relatively high and low current responsive device comprising an elongated current conducting member having thermal responsive material inside thereof, a tubular current conducting heater member surrounding said first member and extending throughout a substantial length of said first member, a heat conducting connection between one end of said tubular heater member and said first member, and electric means for simultaneously passing heating current through said members thereby to heat said material to produce response thereof in a relatively short time interval substantially by the heating effect of the inner member when the current is relatively high and in a longer time in- 8 terval by the `ioint heating effects of both members when the current is relatively low.

3. A relatively high and low current responsive device comprising a tubular member made of thermally responsive material, means securing one end of said member, a second tubular electric heater member surrounding said rst member, and means for producing electric heating currents in both said members thereby to heat said first member to effect a predetermined movement of the other end of said first member in a relatively short time interval when the current is high and in a relatively longer time interval when the current is low.

4. A relatively high and low current responsive device comprising an elongated current conducting tubular member made of thermally responsive material, means securing one end of said member, a second tubular current conducting heater member surrounding said rst member and spaced therefrom, Said second member being conductively connected to said first member at the other end thereof, and a winding surrounding said first member for inducing electric heating currents in said members thereby to heat said first member in a relatively short time interval when the current is high and in a relatively longer time interval when the current is low to produce a predetermined movement of the other end of said first member.

5. A relatively high and low current responsive device comprising an elongated current conducting heater member having an expansible element made of thermally responsive material inside thereof, means securing one end of said element, a tubular current conducting heater member surrounding said rst heater member and having a heat conducting connection therewith, and means including said connection for passing heating current through both said heater members in series thereby to heat said element to effect a predetermined movement of the other end thereof in a relatively short time interval by the heating effect of the inner member when `the current is high and in a relatively long time interval by the joint heating effect of both members when the current is low.

6. A current responsive device comprising a support made of thermally expansible metal, a rod made of thermally expansible metal, an insulating connection between one end of the said rod and one end of said support so that said rod extends lengthwise of said support, a lever pivotally mounted on the other end of said support, a spring biasing said lever for turning movement in a predetermined direction, a connection between the other end of said rod and one end of said lever whereby said rod holds said lever against the force applied by said spring and said rod is maintained under tension upon like changes in length of both said support and said rod caused by changes in ambient temperature. and resistance heating means for said rod including a bare current-conducting heater tube surrounding said rod.

'7. A relatively high and low current responsive device comprising inner and outer tubular resistance heaters, an electric connection between two adjacent ends of said heaters, electric connections for the opposite ends of said heaters for connecting said heaters in series with each other in an electric circuit, and a member of thermally responsive material extending through said inner heater so as to be heated in a relatively short time interval substantially by the heating effect of the inner heater when the current is relatively high and in a longer time interval by the Joint heating effects of both heaters when the current is relatively low.

8. A relatively high and low current responsive device comprising inner and outer. bare tubular resistance heaters, an electric and mechanical heat conducting connection between two adjacent ends of said heaters, electric connections for the opposite ends of said heaters for connecting said heaters in series with each other in an electric circuit, and a member of thermally responsive material extending through 4said inner heater so as to be heated by said heaters in a relatively short time interval substantially by the heating eiect of the inner heater when the current is relatively high and in a longer time interval by the joint heating effects of both heaters when the current is relatively low.

9. A relatively high and low current responsive operating device comprising two concentrically arranged tubular resistance heaters spaced apart radially, an electric and mechanical connection between two adjacent ends of said heaters, electric connections for the opposite ends of said heaters for connecting said heaters in an electric circuit in series with each other, a tension member of thermally expansible material extending through the inner one of said heaters for responding in a relatively short time interval substantially to the heating effect of the inner heater when the current is relatively high and in a longer time interval to the joint heating effects of both heaters when the current is relatively low, a fixed support for one end of of said member and biased to maintain the f member under tension.

10. A variable current responsive operating device comprising spaced inner and outer concentrically arranged bare tubular resistance heaters, an electric and mechanical connection between two adjacent ends of said heaters, said inner heater being longer than said outer heater and having a portion at its opposite end projecting from the opposite end of said outer heater, a magnet core surrounding said projecting portion of said inner heater, electric connections for the opposite ends of said heaters for connecting them in an electric circuit in series with each other, a member of thermally responsive material extending through said inner heater, a xed support for one end of said rod, motion converting mechanism having a rotatable member connected to be operated by the rectilinear movement of the end of said member upon a predetermined ex' pansion of said member, and a centrally pivoted armature mounted to be attracted by said magnet core and connected to rotate said rotatable member in response to a predetermined current in said inner heater independently of the expansion of said thermally responsive member.

ll. In a tripping mechanism` for a circuit breaker biased to the open circuit position and provided with latching means for holding it in the closed circuit position, a rotatable member rotatable in a predetermined direction to effect operation of said latching means to release the circuit breaker, a lever for rotating said member, means biasing said lever for movement to rotate said member in said predetermined direction, a. thermally responsive tension element connected to said lever thereby to hold the lever against movement in said predetermined direction by said biasing means', and heating means for said .expansible tension element connected to said lever thereby to hold said lever against movement in said predetermined direction by said spring. and heating means for said thermally responsive member adapted to be connected in a circuit controlled by the circuit breaker and including a' pair of series connected concentric tubular resistance heaters surrounding said tension element.

13. In a tripping mechanism for a circuit breaker biased to the open circuit position and provided with latching means for holding it in the closed circuit position, a rotatable member rotatable in a predetermined direction to effect operation of said latching means to release the circuit breaker, a lever having ofi-center engagement with said member to rotate said member, a spring for biasing said lever to rotate said member in said predetermined direction, an elongated thermally responsive tension element connected to said lever thereby to hold said lever against movement by said spring, heating means for said thermal member comprising a tubular resistance heater surrounding said thermal member, a magnet core surrounding said heater, means adapted for connecting said heater in a circuit controlled by the circuit breaker, a centrally pivoted armature for said magnet core, and means movable by said armature when the armature is moved to its attracted position in response to a predetermined current in said heater for effecting the rotation of said rotatable member whereby to release the circuit breaker independently of the thermally responsive tension element.

14. In a tripping mechanism for a circuit breaker biased to the open circuit position and provided with latching means for holding it in the closed circuit position, a rotatable member for releasing said latching means, a pivoted element movable in a predetermined direction about its pivot to eiect operation of said rotatable member whereby to release the circuit breaker, a spring for biasing said element in said predetermined direction, a, thermally responsive rod, means securing one end of said rod, a connection between the other end of said rod and said element whereby the rod is maintained under tension and the element is held by said rod against movement by said spring, heating means surrounding said rod comprising spaced inner and outer concentrically arranged tubular resistance heaters and surrounding said rod, an electric and mechanical connection between two adjacent ends of said heaters, said inner heater being longer than said outer heater and having a p0rtion at its opposite end projecting from the opposite end of said outer heater, a magnet core surrounding said projecting portion of said inner heater, electric connections for said opposite ends of said heaters adapted for connecting them in series with each other in a circuit controlled by REFERENCES CITED The following references are oi' record in the tile of this patent:

Number UNITED STATES PATENTS Name Date Weed Feb. 11, 1913 Neahr Mar. 6, 1917 Bush Dec. 31, 1935 Lingal July 14, 1936 Lingal Jan. 17, 1939 Jennings Sept. 7, 1943 Landon June 27, 1944 Millerwise July 11, 1944 

